Oxidatively auto-inhibitive compounds



United States Patent 3,112,273 GXTDATIVELY AUTO-lNHlBlTll E CGMPQ'UNDS Abraham'lviertwoy, Ellrins Park, and Mendel l. Trachtman and Henry Gisser, Philadelphia, Pa, assignors to the United dtates of America as represented by the Secretary of the Army No Drawing. Filed Get. 5, 1960, Ser. No. 128,276

1 Claim. (Cl. 252-62) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or (for the Government for governmental purposes without the payment to us of any royalty there- This invention is a continuation-in-part of our co-pending patent application, Serial Number 777,539, filed November 25, 1958, now abandoned, and relates to fluids and lubricants which are resistant to oxidation and has for an object the use of fluids or lubricants which are oxidatively auto-inhibitive.

Lubricants, (for example, are generally subject to deterioration as a result of oxidation which takes place when the lubricant is exposed to air or oxygen over long periods of time. The products of oxidation may be corrosive acids, sludges, or other products which either interfere with the operation of or cause injury to lubricated instruments or mechanisms which are kept in storage for long periods of time, or are used over long periods without relubrication. Oxidation takes place via a free radical chain mechanism which includes reaction with oxygen, the end products of which may be acids, gums, sludges, etc. To stop this chain reaction, and slow down the rate of oxidative deterioration of the lubricant, oxidation inhibitors are added. The oxidation inhibitors react with or otherwise stablize the free radical chain carriers and thus break the oxidation chain. As a result the lubricant is more stable to oxidation than it would be in the absence of an inhibitor. The addition of oxidation inhibitors, however, does not completely solve the problem. The amount of inhibitor that can be added to a lubricant is limited by solubility considerations, and by the efiect that high concentrations of the inhibitor would have on the other physical and chernioal properties of the lubricant such as viscosity, freezing point, etc. In addition, an increase in concentration of the inhibitor does not necessarily result in an increase in protection against oxidation. In any case when the inhibitor is used up it no longer offers any protection to the lubricant against oxidation, and oxidation generally proceeds at a rapid rate. The use of inhibitor also complicates manufacture of the lubricant since quality control checks are necessary in order to insure that the inhibitor has not been inadvertently left out of the lubricant mix.

We have discovered a class of compounds which are inherently auto-inhibitive to oxidation and in which the entire bulk of the fluid serves as a potential supply of oxidation inhibitor, while at the same time having no deleterious effect on its other characteristics. These compounds have the following typical structure:

RAB-R Aryl where R and R are straight or branched chain groups, or

' other organic configuration, such that the resulting compound is a fluid, and the configuration of the aryl group is such that upon oxidation an aryl-OH is formed which is an oxidation inhibitor. A typical aryl group is p-methoxyphenyl or phenylamine. Upon oxidation one of the first products formed is aryl-OH, and this being an oxidation inhibitor, suppresses further oxidation. The compound is thus autoinhibitive to oxidation. Thus no addi- 3,112,273- Patented Nov. 26, 1963 ice 2 tional oxidation inhibitor is needed and the compound is inherently stable to oxidation. The mechanism whereby these compounds form oxidation inhibitors when oxidized is illustrated below using 1-methyl-l-p-methoxyphenylbutane as an example:

omo-on oaks o-om-ormcm The compounds we have prepared are not only autoinhibit-ive, but when mixed with other compounds which are not stable to oxidation, serve as inhibitors in these compounds.

Tests have shown that at least 5% of the auto-inhibitive compound is necessary in order to insure the production of enough oxidation inhibitor to give satisfactory results. As aforementioned however, the auto-inhibitive compound may be used by themselves if desired.

There are numerous methods of preparing compounds having the desired structure. The following is the method that was used to prepare 1-methyl-1-pamethoxyphenylbutane:

Two thousand milliliters of petroleum ether (boiling point 65 -110 C.); 283 grams (2.62 moles) of anisole and 231 grams (2.62 moles) of pentanol-2 were placed in a 3-liter round bottom flask equipped with a mechanical stirrer and reflux condenser. Three hundred and fifty grams (2.62 moles) of anhydrous aluminum chloride were added to the stirred mixture over a period of one hours. The mixture was then allowed to stand at room temperature for 24 hours, after which it was heated with stirring for 4 hours at 4050 C. The reaction mixture was then allowed to come to room temperature and poured into one liter of ten percent hydrochloric acid. The lower aqueous layer was discarded, and the petroleum ether layer was washed repeatedly with one liter portions of distilled water to remove free acids (3-5 washings were found to be necessary). The petroleum ether solution was dried overnight with anhydrous calcium chloride, filtered then the petroleum ether distilled. The residue was then distilled at 3.5 mm. using an oil pump, the material being collected at 7883 C. The material was redistilled and collected at 81-82 C. at 3.5 mm.

The yield was grains. 7

It is to be understood that although our pursuits were directed toward lubricants, the compounds disclosed may be used to advantage in other materials where high oxidation stability is desirable. Typical of these other materials are power transmission fluids, damping fluids, etc.

We claim: A method for improving the resistance to oxidation of lubricating fluids comprising adding to said fluids at least 5% by weight of 1-methyl-1-p-methoxypheny1=butane.

References Cited in the file of this patent UNITED STATES PATENTS 

